1. Field of the Invention
The present invention relates to a power generator, a timepiece and electronic device having the power generator and a cogging torque adjustment method for the power generator, the power generator being adapted for supplying power in an electronic clock etc. More specifically, it relates to a technique for optimizing a cogging torque (non-excitation torque/detent torque of a step motor) of a power generator.
2. Description of the Related Art
As shown in FIG. 1, an electronic clock with a crystal oscillator as a time standard has a power supply 10 having a small-size power generator 20 and a secondary power supply 30. The power supply 10 actuates a step motor etc. of a processor 14. As shown in FIG. 2, the small-size power generator 20 is provided with a rotor 21 to be rotated by a transmitted rotary drive force, a stator 22 sandwiching the rotor 21 and a power-generating coil 23 wound around a magnetic core constituting a magnetic circuit together with the stator 22 and the rotor 21. The rotor 21 has a power-generating gear train 60 for speeding up and transmitting a rotation of an oscillating weight 25.
In order for the rotor 21 to remain at a desired position when no load is applied, outer notches 221 and 222 for the magnetic saturation portion on a periphery of the rotor 21 are formed on the stator 22 as shown in FIG. 14. The rotor 21 is a permanent magnet having N and S magnetic poles. When the rotor 21 remains at a certain angular position and the rotation of the oscillating weight 25 is transmitted through the power-generating gear train 60, the magnetic poles N and S are rotated to generate electromotive force to the power-generating coil 23. Since a cogging torque is applied to the rotor 21, the rotor 21 is biased to remain at a predetermined angular position (rotor stop position without applying load-referred to xe2x80x9cno-load rotor stop positionxe2x80x9d hereinafter.).
Accordingly, in order to rotate rotor 21 the oscillating weight 25 has to be capable of transmitting greater torque to the rotor 21 than the cogging torque .
However, the size and thickness of respective components of an electronic clock have been reduced to minimize its overall thickness. Thus, the size and weight of the oscillating weight 25 of the small-size power generator 20 are necessarily reduced. Accordingly, with the conventional small-size power generator 20, when the size and weight of the oscillating weight 25 are reduced while the magnitude of the cogging torque applied to the rotor 21 does not change, rotation of the oscillating weight 25 can be hampered, thus rendering it incapable of charging the secondary power supply 30.
In another type of power generator, the rotor of the power generator is rotated by a mechanical energy source such as a power spring. However, when the size of the power spring etc. is reduced, the rotation of the rotor can be hampered, thus causing the same problem in charging the secondary power supply.
Accordingly, it has been desired that the magnitude of cogging torque is made as small as possible so as to facilitate rotation of the rotor even when the size of the oscillating weight 25 and the power spring etc. is reduced.
An object of the present invention is to provide a power generator capable of efficiently reducing the cogging torque applied to the rotor and thus capable of efficiently generating electric power by improving rotation startability of the rotor, a timepiece and electronics having the power generator and a cogging torque adjustment method of power generator.
A power generator according to the present invention includes: a rotor having a permanent magnet rotated by a transmitted rotary drive force; a stator having a rotor accommodation hole for the rotor to be disposed; and a power-generating coil wound around a magnetic core constituting a magnetic circuit along with the stator and the rotor, where magnetic reluctances of a first magnetic circuit extending from the rotor through the stator and the magnetic core back to the rotor and a second magnetic circuit with magnetic flux thereof closing around a stator adjacent the rotor are compared without forming an inner notch on an inner periphery of the rotor accommodation hole, where, when the magnetic reluctance of the first magnetic circuit is smaller, the inner notch is formed on the inner periphery of the rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the first magnetic circuit at a rotation center of the rotor, and where, when the magnetic reluctance of the second magnetic circuit is smaller, the inner notch is formed on the inner periphery of the rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the second magnetic circuit at a rotation center of the rotor.
In the present invention, the inner notch is not restricted to a cut portion formed on the inner periphery of the rotor accommodation hole, but may be a dent (reduced thickness of a part of the stator) on the inner periphery of the rotor accommodation hole or alternatively may be a hole (a through-hole penetrating the stator in thickness direction) formed adjacent to the inner periphery of the rotor accommodation hole. In other words, any arrangement is possible for the inner notch as long as the inner notch can enlarge a part of the gap between the rotor and the inner periphery of the rotor accommodation hole or the through-hole is provided to the magnetic circuit to adjust the magnetic reluctance of the magnetic circuit.
When the stator is, for instance, divided at the rotor accommodation hole section, the first magnetic circuit starts from the rotor (magnet), passes through one of the stators and the magnetic core to the other stator and returns back to the rotor. Similarly, when the stator is integrally formed without being divided, the first magnetic circuit starts from the rotor, passes through the stator on one side of the rotor and the magnetic core to the other side of the stator and returns back to the rotor.
The magnetic flux direction of the second magnetic circuit at the rotation center of the rotor (referred to the second magnetic circuit direction hereinafter) is a direction for the second magnetic circuit with magnetic flux thereof closing at the stator around the rotor, which is ordinarily a direction orthogonal to the magnetic flux direction of the first magnetic circuit at the rotation center of the rotor (referred to the first magnetic circuit direction hereinafter).
The cogging torques by the main first magnetic circuit and the second magnetic circuit with its magnetic flux closing around the rotor are applied to the rotor. Since the respective magnet circuits ordinarily cross perpendicularly at the rotor section, the magnetic circuit that applies a strong magnetic attraction force due to high magnetic flux density, i.e. the magnetic circuit with smaller magnetic reluctance, exerts a large influence. Accordingly, by forming the inner notch in the magnetic circuit having the smaller magnetic reluctance to enlarge the gap between the rotor and the stator to increase magnetic reluctance, the magnetic attraction force applied to the rotor, i.e. the cogging torque can be reduced. Therefore, even when the size and weight of the oscillating weight or the power spring are reduced by reducing the thickness of devices, power can be efficiently generated and the secondary power supply can be efficiently charged. Further, since the actuation torque of the rotor can be reduced when a power spring is used, duration of the power spring can be lengthened with the power spring of the same size, so that the power generator can be worked for a longer time.
Incidentally, when the inner notch is arranged beyond xc2x145xc2x0 disposition relative to either the first or the second magnetic circuit direction having the smaller magnetic reluctance, the magnetic reluctance of either the first or the second magnetic circuit direction having smaller magnetic reluctance cannot be enhanced by the inner notch, so that the cogging torque cannot be reduced. Accordingly, the inner notch has to be formed at least within an angular range of xc2x145xc2x0 around the magnetic circuit direction having smaller magnetic reluctance.
In another aspect of the present invention, a power generator includes: a rotor having a permanent magnet rotated by a transmitted rotary drive force; a stator having a rotor accommodation hole for the rotor to be disposed; and a power-generating coil wound around a magnetic core constituting a magnetic circuit along with the stator and the rotor, where a magnetic reluctance of a first magnetic circuit extending from the rotor through the stator and the magnetic core back to the rotor is set smaller than a second magnetic circuit with magnetic flux thereof closing around a stator adjacent to the rotor when an inner notch is not formed on an inner periphery of the rotor accommodation hole of the stator, and where the inner notch is formed on the inner periphery of the rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the first magnetic circuit at a rotation center of the rotor.
In still another aspect of the present invention, a power generator includes: a rotor having a permanent magnet rotated by a transmitted rotary drive force; a stator having a rotor accommodation hole for the rotor to be disposed; and a power-generating coil wound around a magnetic core constituting a magnetic circuit along with the stator and the rotor, where a magnetic reluctance of a second magnetic circuit with magnetic flux thereof closing around a stator adjacent to the rotor is set smaller than a first magnetic circuit extending from the rotor through the stator and the magnetic core back to the rotor when an inner notch is not formed on an inner periphery of the rotor accommodation hole of the stator, and where the inner notch is formed on the inner periphery of the rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the second magnetic circuit at a rotation center of the rotor.
According to the above power generator, the cogging torque applied to the rotor can be efficiently reduced by forming the inner notch on the magnetic path of the magnetic circuit having the smaller magnetic reluctance among the two magnetic circuits, so that power can be efficiently generated and the secondary power supply can be efficiently charged even when the size and weight of the oscillating weight or the power spring are reduced by reducing the thickness of devices.
In the above arrangement, the inner notch may preferably be formed within an angular range of xc2x110xc2x0 around the magnetic flux direction of either the first magnetic circuit or the second magnetic circuit at the rotation center of the rotor. Accordingly, the cogging torque can be further efficiently reduced as compared to wider angular range arrangement.
Further, the inner notch may preferably be formed in the magnetic flux direction of either the first magnetic circuit or the second magnetic circuit at the rotation center of the rotor. Accordingly, the cogging torque can be reduced with the highest efficiency. Further, by efficiently reducing the cogging torque, the size of the inner notch can be reduced.
In a further aspect of the present invention, a power generator includes: a rotor having a permanent magnet rotated by a transmitted rotary drive force; a stator having a rotor accommodation hole for the rotor to be disposed; and a power-generating coil wound around a magnetic core constituting a magnetic circuit along with the stator and the rotor, where magnetic reluctances of a first magnetic circuit extending from the rotor through the stator and the magnetic core back to the rotor and a second magnetic circuit with magnetic flux thereof closing around a stator adjacent the rotor are compared without forming an protrusion on an inner periphery of the rotor accommodation hole, where, when the magnetic reluctance of the first magnetic circuit is greater, the protrusion projecting toward the rotor is formed on the inner periphery of a rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the first magnetic circuit at a rotation center of the rotor, and where, when the magnetic reluctance of the second magnetic circuit is greater, the protrusion projecting toward the rotor is formed on the inner periphery of the rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the second magnetic circuit at a rotation center of the rotor.
In the present invention, any protrusion can be used as long as the gap between the rotor and the inner periphery of the rotor accommodation hole can be partially reduced, thus adjusting the magnetic reluctance of the magnetic circuit.
The cogging torques by the main first magnetic circuit and the second magnetic circuit with its magnetic flux closing around the rotor are applied to the rotor. Since the respective magnet circuits ordinarily cross perpendicularly at the rotor section, a balance of the magnetic flux density, i.e. a balance between the magnetic reluctance of the respective magnetic circuits exerts great influence. Accordingly, by forming the protrusion in the magnetic circuit having greater magnetic reluctance to reduce the gap between the rotor and the stator to decrease its magnetic reluctance, the magnetic attraction force applied to the rotor, i.e. the cogging torque can be reduced in total. Therefore, even when the size and weight of the oscillating weight or the power spring are reduced by reducing the thickness of devices, power can be efficiently generated and the secondary power supply can be efficiently charged. Further, since the actuation torque of the rotor can be reduced when a power spring is used, duration of the power spring can be lengthened with the power spring of the same size, so that the power generator can be worked for a longer time.
Incidentally, the arrangement of the protrusion may preferably be within an angular range of xc2x145xc2x0 around the magnetic flux direction of either the first magnetic circuit or the second magnetic circuit having the greater magnetic reluctance at the rotation center of the rotor as in the inner notch. Considering cogging torque reduction effect, the angular range may preferably be within xc2x110xc2x0 and the effect can be maximized by forming the protrusion in the magnetic flux direction.
The power generator may preferably further include an oscillating weight for rotating together with body motion of a user; and a power-generating gear train for rotating the rotor by transmitting a rotation of the oscillating weight to the rotor.
Though the rotary drive force for rotating the rotor may be supplied from mechanical energy source such as power spring, rubber, spring and eccentric weight, an oscillating weight rotating together with body motion of a user may preferably be used, since the rotor can be conveniently rotated by simply attaching the power generator to a moving body (e.g. a person""s wrist).
A timepiece according to the present invention has the above power generator and a processor for actuating a time display by an electric energy generated by the power generator.
The timepiece having the power generator can efficiently reduce the cogging torque applied to the rotor, so that the power can be efficiently generated and the secondary power supply can be efficiently charged even when the size and weight of the oscillating weight and the power spring are reduced on account of thickness reduction of a device, thus capable of being applied to a small-size timepiece such as a wristwatch.
An electronic device according to the present invention has the above power generator and a processor actuated by an electric energy generated by the power generator. Such electronic device includes a cellular phone, PHS (personal handyphone system), automobile and house key (including a processor for light and keyless entry), radio, personal computer, calculator, IC card etc. The present invention can be suitably applied to any small-size portable electronic device.
A cogging torque adjustment method according to the present invention is for a power generator including a rotor having a permanent magnet rotated by a transmitted rotary drive force, a stator having a rotor accommodation hole for the rotor to be disposed, and a power-generating coil wound around a magnetic core constituting a magnetic circuit along with the stator and the rotor. The method has the steps of: comparing magnetic reluctances of a first magnetic circuit extending from the rotor through the stator and the magnetic core back to the rotor and a second magnetic circuit with magnetic flux thereof closing around a stator adjacent the rotor without forming an inner notch on an inner periphery of the rotor accommodation hole; forming the inner notch on the inner periphery of the rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the first magnetic circuit at a rotation center of the rotor when the magnetic reluctance of the first magnetic circuit is smaller; and forming the inner notch on the inner periphery of the rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the second magnetic circuit at a rotation center of the rotor when the magnetic reluctance of the second magnetic circuit is smaller.
Another cogging torque adjustment method according to the present invention is for a power generator including a rotor having a permanent magnet rotated by a transmitted rotary drive force, a stator having a rotor accommodation hole for the rotor to be disposed, and a power-generating coil wound around a magnetic core constituting a magnetic circuit along with the stator and the rotor, the method comprising the steps of: comparing magnetic reluctances of a first magnetic circuit extending from the rotor through the stator and the magnetic core back to the rotor and a second magnetic circuit with magnetic flux thereof closing around a stator adjacent the rotor without forming an protrusion on an inner periphery of the rotor accommodation hole; forming the protrusion projecting toward the rotor on the inner periphery of a rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the first magnetic circuit at a rotation center of the rotor when the magnetic reluctance of the first magnetic circuit is greater; and forming the protrusion projecting toward the rotor on the inner periphery of the rotor accommodation hole of the stator within angular range of xc2x145xc2x0 around a magnetic flux direction of the second magnetic circuit at a rotation center of the rotor when the magnetic reluctance of the second magnetic circuit is greater.
In the above cogging torque adjustment method of the power generator, arrangement of the rotor and the stator has been described thus far, and arrangement of the inner notch and the protrusion has also been described.
The cogging torque can be efficiently reduced according to the cogging torque adjustment method of the present invention.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.